1. Slide 1 GSOP Workshop, Reading, 31 Agust-1 September 2006 Temperature, Salinity and Sea Level: climate variability from ocean reanalyses (Intercomparison Items 3 & 4) Magdalena A. Balmaseda Anthony Weaver

2. Slide 2 GSOP Workshop, Reading, 31 Agust-1 September 2006 Outline Defining the variability: signal and noise -Seasonal cycle removed: Anomalies with respect to the common period (1994-2000) -12-month/3-month running mean -Focus on the upper ocean (upper 300m): Equator, Mid latitudes Temperature and salinity: -What can we say about climate variability? -Time variation of uncertainty -Outliers? Source of uncertainty (forcing, model, assimilation method)? Sea Level variations: volume or mass changes? Summary and conclusions

3. Slide 3 GSOP Workshop, Reading, 31 Agust-1 September 2006 Focus Regions for Items 3 & 4

4. Slide 4 GSOP Workshop, Reading, 31 Agust-1 September 2006 Uncertainty in the Mean Ambiguity in the definition closest level, interpolated values…? Real Uncertainty? We will use anomalies…

5. Slide 5 GSOP Workshop, Reading, 31 Agust-1 September 2006 T300: Equatorial regions Eq Pac: Uncertainty decreases with time. Relatively robust interannual variability. Increased uncertainty after 2000. Why? Eq Indian: Uncertainty remains large throughout the record. Signal to noise <1. Outliers This is also the case for the Eq Atlantic

6. Slide 6 GSOP Workshop, Reading, 31 Agust-1 September 2006 What can we say about Tropical variability? How should we interpret the outliers? Need to understand the reasons An outlier for the good reason is very valuable An outlier for the wrong reason is damaging

7. Slide 7 GSOP Workshop, Reading, 31 Agust-1 September 2006 T300: Mid latitudes (northern) The North Atlantic is dominated by a warming trend, especially post 1997 Large uncertainty after 2000. Phase/amplitude of decadal variability is poorly resolved. The North Pacific does not show a warming trend, but more of a rapid shift in the early 90’s Large uncertainty after 2000 Phase/amplitude of decadal signal is poorly resolved. Outliers.

8. Slide 8 GSOP Workshop, Reading, 31 Agust-1 September 2006 GLOBAL SIGNALS GLOBAL: Upper T-300m GLOBAL Upper T-750m GLOBAL Upper T-3000m Warming occurs ~ in first 750m

9. Slide 9 GSOP Workshop, Reading, 31 Agust-1 September 2006 Salinity Variability Salinity variability dominated by spin-up effects in several cases. There is no consistency among reanalyes

10. Slide 10 GSOP Workshop, Reading, 31 Agust-1 September 2006 Signal/Noise Ratio (long period) EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL T300-12m-rmT750-12m-rmT3000-12m-rm S300-12m-rmS750-12m-rmS3000-12m-rm

11. Slide 11 GSOP Workshop, Reading, 31 Agust-1 September 2006 Signal/Noise Ratio (Short period, interannual) EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL T300-3m-rmT750-3m-rmT3000-3m-rm S300-3m-rmS750-3m-rmS3000-3m-rm

12. Slide 12 GSOP Workshop, Reading, 31 Agust-1 September 2006 Sources of Uncertainty All ERA40 ERA40-No data ERA40-Assim

13. Slide 13 GSOP Workshop, Reading, 31 Agust-1 September 2006 Equatorial Atlantic: Assimilation increases spread All ERA40 ERA40-No data ERA40-Assim

14. Slide 14 GSOP Workshop, Reading, 31 Agust-1 September 2006 Assimilation and Uncertainty T300 Long period 1956-2005: Assimilation decreases uncertainty everywhere Latest period 1993-2005 Only in EQPAC the assimilation reduces uncertainty 1956-2005 1993-2005 EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL

15. Slide 15 GSOP Workshop, Reading, 31 Agust-1 September 2006 Assimilation and Uncertainty S300 Long period 1956-2005: Assimilation increases uncertainty everywhere Latest period 1993-2005 Assimilation increases uncertainty 1956-2005 1993-2005 TRATL NPAC NATL GLOBAL EQPAC EQATL EQIND TRPAC

16. Slide 16 GSOP Workshop, Reading, 31 Agust-1 September 2006 GLOBAL SEA LEVEL VARIATIONS I Prior to 2002, changes in sea level and steric height are correlated: Volume rather than mass Changes in bottom pressure are not consistent amont analyses?

17. Slide 17 GSOP Workshop, Reading, 31 Agust-1 September 2006 GLOBAL SEA LEVEL VARIATIONS II Temperature contribution to dynamic height dominates the trend

18. Slide 18 GSOP Workshop, Reading, 31 Agust-1 September 2006 Sea level variations: Seasonal cycle Seasonal variations in global sea level are attributed to mass variations that affect the bottom pressure.

19. Slide 19 GSOP Workshop, Reading, 31 Agust-1 September 2006 Summary and Conclusions There is large uncertainty in climate signals -Signal to noise ratio > 1 in the Eastern Pacific for Temperature -Signal to noise ratio <1 for salinity in most regions -Warming trend in the 90’s is consistently reproduced -What is happening now? There is not consistent picture Forcing fluxes and analysis methods are largest source of uncertainty -Data Assimilation does not always collapse the spread: We need to pay more attention to the assimilation methods. Global Sea level trends -1993-2002: Consistently attributed to temperature rise. -2002-present: It is not clear. Mass increase? -Seasonal variations related to mass variations.

20. Slide 20 GSOP Workshop, Reading, 31 Agust-1 September 2006 NEXT Web page to collect. WHERE? GSOP web page? Maps of signal to noise ratio, and so on Need to define the variables so there are not “so” dependent on the vertical model grid. There are currently 20 analysis… are there more there? Agreement on colour coding and naming convention? Other?